Explosion proof hand held instrument



June 13, 1967 W. A. DOUGLAS EXPLOSION PROOF HAND HELD INSTRUMENT Filed June 5,

NR N mm .& Q

INVENTOR. W/ZZ/AM 001/6245 BY 4% 7 III/[1111A United States Patent 3,325,659 EXPLOSION PROOF HAND HELD INSTRUMENT William A. Douglas, South Pasadena, Calif., assignor to The Mira Corporation, Los Angeles, Calif., a corporation of California Filed June 5, 1964, Ser. No. 373,004 7 Claims. (Cl. Sill-d) The present invention relates to electrical equipment and, more particularly, to a watertight, explosion pro-of power instrument.

The use of power instruments, such as power drills, is frequently desirable in environments that contain explosive gases. Also, it is often desired that such a power instrument be watertight. In some applications, it is also desirable that the power instrument be capable of being autoelaved. For example, surgical power instruments, such as bone drills, should be capable of safe use in operating and other rooms where anesthetic gases are present, and of periodical sterilization in an autoclave.

In the past, several attempts have been made to create a power instrument that could be safely used in environments of the type mentioned above. One advanced instrument of this type is the self-powered surgical drill disclosed in US. Patent 3,120,845 of David B. Horner.

However, these prior art instruments still had the disadvantage that explosive gases and sterilizing fluids could in certain instances reach electrical parts and that explosions could propagate themselves to the outside of the power instrument.

Also, some prior art power instruments had the electric battery located in the handle, so that the overall configuration of the handle was dictated by the dimensions of the battery, rather than being styled according to the users best convenience.

The subject invention realizes the above-mentioned desiderata and overcomes the latter disadvantages.

From a broad aspect thereof, the invention provides a watertight, explosion proof power instrument for driving a tool, such as a drill, comprising a housing having a lateral handle and defining a first bore extending at an angle, such as an angle between 40 to 80 to the handle, and a second bore extending substantially parallel to the first bore. The first bore is dimensioned to house an electric drive, and the second bore to receive an electric battery for energizing the drive. In this manner, the handle need not be adapted to the configuration of the battery, but can be styled to be conveniently held by the users hand. Also, the size of the battery is not limited by the dimensions of the handle.

The power instrument of the invention also includes a shaft driven by the electric drive and extending from inside the housing to the outside thereof. A shaft seal is located at the shaft and provides an explosion proof labyrinth path between the inside of the housing and the environment thereof. The first bore is sealably closed and means are provided for closing the second bore and providing an explosion proof labyrinth path between the second bore and the environment of the housing. If desired, the power instruments may comprise means for closing the first bore and providing an explosion proof labyrinth path between this bore and the outside of the housing.

In a preferred embodiment of the invention, the power instrument includes an electric switch located in the abovementioned housing for selectively connecting the electric drive to the battery. The power instrument also includes a rod for actuating the electric switch. The rod extends through a closely fitting bore in the housing, dimensioned to provide a flame path of at least three-quarter inches in length. In this manner, a spark or flame occurring at the switch cannot propagate itself through the housing, as

3,325,659 Patented June 13, 1967 in some prior art apparatus in which the switch could rather freely be reached by explosive gases. Also, the arrangement just described prevents damage to the switch during autoclaving. Means are provided on the power instrument for selectively reciprocating the switch actuating rod.

In another preferred embodiment of the invention, the power instrument includes relatively stationary terminals mounted in the above-mentioned second bore. The electric battery which is insertable into this second bore has battery terminals corresponding to the stationary terminals just mentioned. Means, such as a spring, are located at the stationary terminals for biasing the battery terminals away from the stationary terminals. The power instrument includes a cap for closing the second bore. This cap is dimensioned to move the battery terminals into current conductive engagement with the stationary terminals. In addition, this cap is constructed to provide an explosion proof labyrinth path between the second bore and the environment of the housing before the battery terminals engage the stationary terminals, while the battery terminals engage the stationary terminals, and while the battery terminals disengage the stationary terminals. In prior art apparatus, the battery terminals would engage tr e corresponding stationary terminals when the battery was being inserted or removed and sparks could then form when the switch was closed. These sparks could lead to a dangerous explosion. The subject invention precludes this severe danger by employing the recited biasing structure.

In another preferred embodiment of the invention, the power instrument is equipped with a planetary reduction gear located in the above-mentioned first bore for transmitting torque from the motor to the tool drive shaft. 1 have found that this type of gear leads to a power instrument that has exceptional low friction losses and high starting torque.

In a further preferred embodiment of the invention, the electric drive comprises an electrical motor having a commutator with associated brushes. The diameter of the first bore in which these parts are located is minimized by employing spiral leaf springs for mounting the brushes against the commutator.

In a further preferred embodiment of the invention, the reduction gear is dimensioned to occupy substantially the cross-section of the first bore so as to jointly define with the shaft a means inhibiting flame propagation from the motor to the environment of the housing. In this manner, an inadvertent flame emerging from the motor is effectively quenched.

In another preferred embodiment of the invention, the shaft seal includes a flange member which is mounted on and encompasses the tool drive shaft. The flange member defines a portion of predetermined diameter at the first bore and a portion of the smaller diameter extending in a direction away from that bore. The shaft seal further includes a cap which is threaded to the housing at the first bore. The cap encompasses the flange member and the shaft and defines bores having inside diameters corresponding to the above-mentioned predetermined and smaller diameters of the flange member. In addition, the shaft seal includes a sealing member which encompasses the shaft and is positioned inside the above-mentioned cap. This sealing member defines a first circumferential sealing surface which engages an annularins-ide portion of the cap, and a second circumferential sealing surface which engages an annular surface of the shaft.

As the description proceeds, it will be recognized that the features so far recited can frequently be used alone or in combination as the purpose and nature of the power instrument may require.

The invention will become more readily apparent from the following detailed description of a preferred embodiment thereof, illustrated by way of example in the accompanying drawings which shows a longitudinal section through a power drill according to the invention.

The power drill in the drawing has a housing which defines a bore 11 and a bore 12. A handle 14, which is only partially illustrated in the drawing, is attached to housing 10 and extends laterally therefrom. Housing 10 and handle 14 are of a material that withstands autoclaving temperatures, such as temperatures of the order of 250 to 300 F. Thus, the housing may be of a suitable material, such as stainless steel, and the handle 14 may be made of high-temperature-resistant rubber.

A motor 15 is located in bore 11. This motor 15 has a shaft 17 which is mounted by bearings 18 and 19 and carries a wound armature 20 with commutator 21. The motor further includes a permanent magnet stator 23 which is preferably formed of a molded ceramic magnetic material to decrease the size thereof. The stator 23 is contained in a cylindrical sleeve 24. The space requirements of motor 15 are further minimized by employing spiral leaf springs 26 for mounting the brushes (not shown) against the commutator 21. The spiral leaf springs 26 are mounted on current conducting posts 27.

The motor shaft 17 is connected to a gearing 28, including a lay gear coupled to -a planetary gear, which practically fills the cross-section of bore 11. This gearing, as such, is of conventional construction so that a detailed description thereof is unnecessary. The lay gearing 28 drives a shaft 29 which is mounted on bearings 30 and 31 and which extends from bore 11 to the outside of housing 10.

The shaft 29 is an external thread 32 on which a tool retaining chuck or similar structure (not shown) may be removably mounted. A circular flange structure 34 is threaded on shaft 29 at the bore 11. Flange 34 defines a portion 35 of predetermined diameter at the bore 11 and a portion 36 of smaller diameter which extends in a direction away from the bore. A cap 38 is threaded to the housing at bore 11. This cap encompasses the flange member 34 and the shaft 32 and has a portion 40 defining an inside diameter corresponding closely to the diameter of flange portion 35, and a second portion 41 defining an inside diameter corresponding closely to the diameter of flange portion '36. A sealing member 42, which encompasses a portion 43 of increased diameter of the shaft 32 and which is located inside the cap 38, is disposed behind flange 34. A helical spring 44 and an annular member 45 retain sealing member 42 in place. A sealing ring 46 associated with member 42 defines a first circumferential sealing surface which engages an annular inside portion of cap 38. A second sealing ring 47 is also associated with member 42 and engages the increased diameter portion 43 of the shaft 32. In addition, a sealing ring 49 seals the cap 38 with respect to the housing 10. The sealing rings 46, 47 and 49 are preferably of high-temperature-resistant material, such as a suitable silicone rubber or a polytetrafluoroethylene compound.

From a consideration of the structure concerning cap 38 and the adjacent parts, it will be recognized that a shaft seal is provided that is not only watertight, but per-' mits autoclaving of the illustrated power drill, and precludes any danger of explosion when the drill is used in an environment that contains explosive gases. More particularly, it will be recognized that the cap 38 provides an explosion-proof labyrinth path 50 where the cap is threaded to the bore 11 by means of an external thread 51. The flame quench path thus provided is very long, since the linear length of threads 51 is in the order of linear feet. In addition, the cap 38, flange member 34, sealing member 42, bearings 30 and 31, and the planetary gear '38 provide a repeatedly obstructed flame quench labyrinth path between motor 15 and the environment of housing 10. This quench path will even be present when which renders the bore 11 watertight and permits autoclaving of the power drill. The seal, as well as any further seal subsequently to be described, should be made of a high-temperature-resistant material, such as silicone rubber or a polytetrafluoroethylene compound.

In the drawing, a battery 56 is shown inserted in the bore 12, which extends substantially parallel to bore 11 and at an angle to handle 14. This battery carries a receptacle 57 with male terminals 58 and 59 that are connected, respectively, to the positive and negative poles of the battery. A mounting block 60 is located in bore. 12 and carries a pair of relatively stationary terminals 62 and 63. A nose 65 projecting from battery 56 and sliding in a longitudinal slot 66 in housing 10 at bore 12 assures spacial correspondence between battery terminals 58 and 59 and stationary terminals or prongs 62 and 63.

An insulated wire 67 connects terminal 62 to the motor 15. The terminal 63 is connected to motor 15 through a switch 68 and an insulated wire 69. A cap 70 closes bore 12 and maintains the battery terminals 58 and 59 in engagement with the stationary terminals 62 and 63. The connection between cap 70 and housing 10 is again rendered watertight by a sealing ring 71 and explosion proof by a threaded connection at 72 which provides a labyrinth path similar to that shown at 50 and 53. One source of danger with a cap arrangement that closes a battery cavity and is of the type just described, resides in the fact that the labyrinth path at 72 is not fully established when the battery 56 is in the process of being removed or inserted. In other words, when the battery 56 is to be removed, the cap 70 has to be unscrewed from housing 10 and the bore 12 Will become successively and eventually fully exposed to the environment of the ower drill. Similarly, when a new battery is being inserted, the bore 12 is initially fully exposed to the explosive gases surrounding the power drill and the labyrinth path 72 is only successively established as the cap 70 is screwed on housing 10. Since there is no guaranty that the switch 68 is open while the battery 56 is replaced, a violent explosion may occur due to sparks generated at terminals 58, 59, 62 and 63.

The subject invention completely precludes this serious danger by providing at terminals 62 and 63 a strong helical spring 75 which acts between mounting block 60 and a shoulder 76 of battery 56 and which biases the battery terminals 58 and 59 away from stationary terminals 62 and 63. This spring 75, as well as the limited length of prongs 62 and 63 afford a positive assurance that sparks at battery terminals 58 and 59 are only generated when the quench path 72 is yet of suflicient length to effectively preclude any flame propagation to the outside of housing 10. In other words, the terminals 58, 59, 6'2 and 63 are forced to disengage after only a few turns of rotation of cap 70, and these terminals can only engage when the placement of the cap has proceeded to an extent sufiicient to provide an adequate labyrinth path 72. It will, of course, be recognized that the corresponding threads on cap 72 and housing '10 should be of sufficient length to take full advantage of the significant safety feature just described.

Access to the switch 68 is provided by a removable cap 77 which is sealed to housing 10 by a sealing ring 78 and which provides a flame quench labyrinth path 73 similar to the paths 50, 53 and 72 described above. The plunger 81 of switch 68 is actuated by an angular member 82 which is pivoted with respect to housing 10 by means of a pin 83 that projects from a block 80 of insulating material that is attached to part 60 and also carries the switch 68. A switch actuator rod 84 extends from -a cavity 85 in housing to the angular member 82. A sleeve 86 of insulating material is located on angular member 82, prevents impingement of actuator rod 84 on metallic parts of angular member 82, and provides an electrical insulation between actuator rod 84 on the one hand, and switch 68, plunger 81, and angular member 82 on the other hand.

For part of its length, the switch actuator rod 84 extends through a closely fitting bore 88 in housing It). The actuator rod 84 and the bore 88 jointly define a very narrow flame quench path which will prevent the propagation of flames from the switch to the outside of housing 10. The length of this path, that is the length of bore 88, should be adapted to the particular safety requirements. Thus, the bore 88 may be of at least three-quarters inch in length,

For the purpose of further safety, that portion of actuator rod 84 which is located at housing cavity 85 has the form of a piston 90 which rides in a closely corresponding bore 91 in housing 10. A sealing ring 92 associated with this piston structure assures watertightness. A spring 94 bears against a shoulder 95 in housing 19 and a shoulder 96 on actuator rod 84 and biases this rod in a direction away from angular member 82. In this manner, the switch 68 is normally kept open, inasmuch as the contact switches of the subject type are biased to the open position when the switch, is not actuated. A reciprocable actuating member 98 of insulating material permits manual actuation of the switch actuator rod 84 and the switch 68. To this end, the handle 14 is provided with an index finger cavity 99 and member 98 is slidable in a cavity 100 jointly defined by housing .10 and handle 14.

Movement of actuating member 98 is transmitted to switch rod 84 by a lever 102 which is pivoted with respect to handle 14 by a pin 183. A slot 105 in member 98 permits slidable movement of this member 98 with respect to pin 103.

When the actuating member 98 is depressed, the switch 68 will be closed and electrical energy will flow from battery 56 to motor 15. Motor will drive the gearing 28, which in turn will rotate the tool shaft 32 and any tool attached thereto. In contrast to the type of gears normally used in power drills, a planetary gear has exceptional low friction losses and low starting torque. The torque produced by motor 15 is, therefore, utilized most effectively. Also, the use of a planetary gear as a portion of the gearing 28 permits placement of motor, gear, and tool shaft in one cylindrical cavity, with resulting reduction of the lateral dimensions of the power drill.

If the actuating member 98 is released, the bias spring 94 will bring about an opening of switch 68, and flame propagation through sparks at switch 68 is most effectively prevented by the safety features described in connection with cap 77 and actuator rod 84.

It will now be recognized that the subject invention provides a multitude of novel and significant concepts which partially alone and partially in combination embody maximum safety of power tools and other types of electrical equipment in areas contaminated with explosive gases and in environments of high temperature and humidity. It is particularly advantageous that equipment incorporating concepts of the subject invention may be rendered germ-free by autoclaving and yet afford all the safety provisions hereinbefore mentioned. In addition, apparatus according to the subject invention may not only be autoclaved but embody features which effectively prevent the migration of bacteria to fully enclosed hollow spaces in the housing or similar migrations from such spaces to the outside of the housing.

In brief, the subject invention provides maximum safety devices of a type not heretofore available.

While a particular type of instrument has been described and illustrated, it will, of course, be recognized that the concepts of the subject invention herein disclosed will have many other applications, and that many modifications within the scope of the subject invention will be apparent to those skilled in the art.

I claim:

1. A watertight, explosion proof, self-powered power tool comprising (a) a housing having first and second bores defined therein and extending substantially parallel to each other in the housing, said housing including a handle mounted therewith to allow manual operation of the .power tool,

(b) tool switch actuating means mounted with said handle for allowing the operator to control the switch and thereby the power tool while holding the tool by the handle,

(c) electric drive means adapted for driving a tool mounted in the first of the housing bores,

(d) a shaft coupled to the drive means to be driven therefrom and extending from the housing proper,

(e) watertight sealing means mounted within said first bore adjacent said shaft,

(f) cap means adapted for closing said first bore, said cap means and coacting portions of the first bore being relatively defined to be interengaged for sealing the first bore and defining an explosion-proof labyrinth path at the surfaces of interengagement,

(g) a pair of electrical contacts mounted adjacent an extremity of the second bore,

(h) electrical switching means mounted in the housing and electrically connected between said contacts and the drive means for controlling the energization of the latter upon operation thereof,

(i) yieldable means mounted in the second bore adjacent the electrical contacis for biasing a battery positioned in the bore away from the electrical contacts,

(j) said second bore being defined to receive and hold electrical battery means for powering the drive means when held in electrical engagement with said contacts,

(k) watertight sealing means mounted on said housing adjacent the battery entry end of the second bore,

(1) cap means for closing the second bore and adapted for holding a "battery in electrical engagement with said contacts when closing the second bore and allowing disengagement when the cap means is moved to a bore opening position,

(m) said latter mentioned cap means and coacting portions of the second bore being relatively defined to be interengaged for sealing the second bore and defining an explosion-proof labyrinth path at the surfaces of interengagement, and

(11) motion transmitting means mounted in the housing between said electrical switching means and the tool actuating means for operating the electrical switchmg means.

2. A watertight, explosion proof, self-powered power tool comprising (a) a housing having first and second bores defined therein and extending substantially parallel to each other in the housing, said housing including a handle mounted therewith to allow manual operation of the power tool,

(b) tool switch actuating means mounted with said handle for allowing the operator to control the switch and thereby the power tool while holding the tool by the handle,

(c) electric drive means adapted for driving a tool mounted in the first of the housing bores,

(d) a shaft adapted for driving a tool coupled to the drive means to be driven therefrom and extending from the housing proper,

(e) watertight sealing means mounted within said first bore,

(f) cap means adapted for closing said first bore, said cap means and coacting portions of the first bore being relatively defined to be interengaged for sealing the first bore and defining an explosion-proof labyrinth path at the surfaces of interengagement,

(g) a pair of electrical contacts mounted adjacent an extremity of the second bore,

(h) electro-mechanical switching means mounted in the housing and electrically connected between said contacts and the drive means for controlling the energization of the latter,

(-i) said second bore "being defined to receive and hold electrical battery means for powering the drive means when held in electrical engagement with said contacts,

(j) watertight sealing means mounted on said housing adjacent the ends of the second bore,

(k) cap means for closing the second bore and adapted for holding a battery in electrical engagement with said contacts when closing the second bore,

(l) said latter mentioned cap means and coact-ing portions of the second bore being relatively defined to be interengaged for sealing the second bore and defining an explosion-proof labyrinth path at the surfaces of interengagement, and

(m) motion transmitting means mounted in the housing between said switching means and the tool actuating means for operating the electrical switching means to thereby energize and de-energize the drive means when a battery is positioned within the second bore.

3. A watertight explosion proof, self-powered power tool as defined in claim 2 wherein said second bore includes battery positioning means constructed and defined relative to battery means to be positioned within the sec- Ond bore to allow the battery means to be inserted only in a preselected fashion to assure the interengagement of the battery and said contacts.

4. A watertight explosion proof, self-powered power tool as defined in claim 3 wherein the battery means comprises an electrical battery having a projecting nose and a pair of battery terminals corresponding to said contacts and said second bore has a longitudinal slot adapted for slidably receiving the projecting nose of the battery.

5. A watertight explosion proof, self-powered power tool as defined in claim 4 including means mounted adjacent said contacts for normally biasing the battery terminals away from said contacts.

6. A watertight explosion proof, self-powered powertool as defined in claim 3 wherein each of said cap means and coacting portions of the housing are threaded relative to one another to provide for the bore closing and having a length to render the tool explosion proof.

7. A watertight explosion proof, self-powered power tool as defined in claim 2 wherein said drive means comprises electric motor means coupled to reduction gearing means for driving said shaft.

References Cited UNITED STATES PATENTS 2,777,963 1/1957 Kuntz 310 3,120,845 1/1964 Horner 31050 3,152,272 10/1964 Hovhanesian 31050 3,173,417 3/1965 Horner 310-50 3,196,298 7 7/1965 Kent 3105O 3,196,299 7/1965 Kott 310--50 MILTON O. HIRSHFIELD, Primary Examiner.

J. W. GIBBS, Assistant Examiner. 

1. A WATERTIGHT, EXPLOSION PROOF, SELF-POWERED POWER TOOL COMPRISING (A) A HOUSING HAVING FIRST AND SECOND BORES DEFINED THEREIN AND EXTENDING SUBSTANTIALLY PARALLEL TO EACH OTHER IN THE HOUSING, SAID HOUSING INCLUDING A HANDLE MOUNTED THEREWITH TO ALLOW MANUAL OPERATION OF THE POWER TOOL, (B) TOOL SWITCH ACTUATING MEANS MOUNTED WITH SAID HANDLE FOR ALLOWING THE OPERATOR TO CONTROL THE SWITCH AND THEREBY THE POWER TOOL WHILE HOLDING THE TOOL BY THE HANDLE, (C) ELECTRIC DRIVE MEANS ADAPTED FOR DRIVING A TOOL MOUNTED IN THE FIRST OF THE HOUSING BORES, (D) A SHAFT COUPLED TO THE DRIVE MEANS TO BE DRIVEN THEREFROM AND EXTENDING FROM THE HOUSING PROPER, (E) WATERTIGHT SEALING MEANS MOUNTED WITHIN SAID FIRST BORE ADJACENT SAID SHAFT, (F) CAP MEANS ADAPTED FOR CLOSING SAID FIRST BORE, SAID CAP MEANS AND COACTING PORTIONS OF THE FIRST BORE BEING RELATIVELY DEFINED TO BE INTERENGAGED FOR SEALING THE FIRST BORE AND DEFINING AN EXPLOSION-PROOF LABYRINTH PATH AT THE SURFACES OF INTERENGAGEMENT, (G) A PAIR OF ELECTRICAL CONTACTS MOUNTED ADJACENT AN EXTREMITY OF THE SECOND BORE, (H) ELECTRICAL SWITCHING MEANS MOUNTED IN THE HOUSING AND ELECTRICALLY CONNECTED BETWEEN SAID CONTACTS AND THE DRIVE MEANS FOR CONTROLLING THE ENERGIZATION OF THE LATTER UPON OPERATION THEREOF, (I) YIELDABLE MEANS MOUNTED IN THE SECOND BORE ADJACENT THE ELECTRICAL CONTACTS FOR BIASING A BATTERY POSITIONED IN THE BORE AWAY FROM THE ELECTRICAL CONTACTS, (J) SAID SECOND BORE BEING DEFINED TO RECEIVE AND HOLD ELECTRICAL BATTERY MEANS FOR POWERING THE DRIVE MEANS WHEN HELD IN ELECTRICAL ENGAGEMENT WITH SAID CONTACTS, (K) WATERTIGHT SEALING MEANS MOUNTED ON SAID HOUSING ADJACENT THE BATTERY ENTRY END OF THE SECOND BORE, (L) CAP MEANS FOR CLOSING THE SECOND BORE AND ADPATED FOR HOLDING A BATTERY IN ELECTRICAL ENGAGEMENT WITH SAID CONTACTS WHEN CLOSING THE SECOND BORE AND ALLOWING DISENGAGEMENT WHEN THE CAP MEANS IS MOVED TO A BORE OPENING POSITION, (M) SAID LATTER MENTIONED CAP MEANS AND COACTING PORTIONS OF THE SECOND BORE BEING RELATIVELY DEFINED TO BE INTERENGAGED FOR SEALING THE SECOND BORE AND DEFINING AN EXPLOSION-PROOF LABYRINTH PATH AT THE SURFACES OF INTERENGAGEMENT, AND (N) MOTION TRANSMITTING MEANS MOUNTED IN THE HOUSING BETWEEN SAID ELECTRICAL SWITCHING MEANS AND THE TOOL ACTUATING MEANS FOR OPERATING THE ELECTRICAL SWITCHING MEANS. 